Increasingly, heavy oil feedstocks such as heavy crude oils, bitumen, tar sands, shale oils, and hydrocarbons derived from liquefying coal are being utilized as hydrocarbon sources due to the decreasing availability of easily accessed light sweet crude oil reservoirs. These heavy oil feedstocks are disadvantaged relative to light sweet crude oils, containing significant amounts of heavy hydrocarbon fractions such as residue and asphaltenes, and often containing significant amounts of sulfur, nitrogen, metals (e.g., vanadium and nickel), and/or naphthenic acids. The concentration of metals in heavy oil feedstocks can vary from a few ppm up to 1,000 ppm or more, with a vanadium to nickel ratio of about 6:1.
The heavy oil feedstocks typically require a considerable amount of upgrading to at least partially convert heavy hydrocarbon fractions into lighter, more valuable hydrocarbons and/or to reduce the metals content, sulfur content, nitrogen content, and/or acidity of the feedstock. As a result, refiners are required to use more catalyst for hydroprocessing heavy oil feedstocks than lighter feedstocks.
A method to upgrade heavy oil feedstock is to disperse a slurry catalyst in the feedstock and pass the feedstock and slurry catalyst together with hydrogen through a slurry-bed, or fluid-bed, reactor operated at a temperature effective to crack heavy hydrocarbons in the feedstock and/or to reduce the sulfur content, nitrogen content, metals content, and/or the acidity of the feedstock. The feedstock and the slurry catalyst move together through the cracking reactor and are separated upon exiting the cracking reactor. Spent slurry catalyst can contain high amounts of metal (specifically, vanadium) and coke deposition.
With the increasing demand and market price for metal values and environmental awareness thereof, the large amount of spent catalysts generated in heavy oil upgrading can serve as a source for metals recovery. In particular, recovery of deposited vanadium is desirable as vanadium has a range of industrial uses.
There is still a need for improved methods to recover deposited metals, such as vanadium, from spent catalysts.